1. Field of the Invention
The present invention relates to an air feed control device for an endoscope which is used to regulate the amount of air to be fed into a cavity such as a cavity of a human body.
2. Description of the Prior Art
Conventional endoscopes are usually equipped with an air feed control device which is adapted to regulate the quantity of air to be fed into a cavity such as a cavity of a human body and which is usually combined with a water feed device for cleaning the objective lens or its cover glass at the distal end of the insertion section of the endoscope to remove soil thereon. Air can also be used to blow off drops of water remaining on the objective lens or cover glass.
There have been proposed air feed control devices of the type having valve means provided with an air vent passage opening to the atmosphere which is adjustably closed by the bulb of a finger of an operator in order to regulate the quantity of air escaping from the vent passage into the atmosphere and hence the quantity of air introduced into the cavity through the air feed nozzle.
A problem in the majority of air feed control devices at present on the market is that even if the vent passage is fully opened in order to bypass air feed from the body cavity, a part of the air is still forced into the body cavity because it is impossible to allow air to escape through the vent passage without giving rise to resistance.
Reference may be made to the following description from which the present state of the art is clearly apparent.
FIG. 7 schematically shows an air feed-water feed control device at present on the market in which a regulating valve means 10 is mounted in the operating section 1 of the endoscope. Valve means 10 selectively connects an intake air pipe 4.sub.2 having its one end connected to an air supply (which is well known in the art and not shown) provided separately from the endoscope, with an outlet air pipe 4.sub.1 connected to an air feed-water feed nozzle 3 at the distal end of the flexible insertion section 2. Flexible section 2 is insertable into a body cavity.
The regulating valve 10 is also so arranged as to be capable of selectively connecting an intake water pipe 5.sub.2 having its one end connected to a water supply (which is also well known in the art and not shown therein) provided separately from the endoscope, with an outlet water pipe 5.sub.1 with its one end connected to the air feed-water feed nozzle 3. One-way valve 8 prevents the counterflow of air.
Specifically, the regulating valve means 10 comprises a valve casing 9 having the shape of a barrel with a cylindrical bore, and a valve body 6 having a vent passage 6' slidably airtightly fitted in the valve casing 9. Within the bore is housed a helical compression spring 7 which continuously urges the valve body 6 up as seen in FIG. 7, so that the intake and outlet air pipes 4.sub.2, 4.sub.1 communicate by the regulating valve means 10. The valve body 6 is further provided with an annular groove 6" around its outer periphery at the axial position where the annular groove 6" is aligned with both of the intake and outlet water pipes 5.sub.1, 5.sub.2 when the valve body 6 is pushed down against the helical compression spring 7.
As seen in FIG. 7, the valve body 6, when forced up, allows the air collected in the valve casing 9 to escape into the atmosphere through the vent passage 6'.
In the air feed-water feed control device of the above-mentioned type, for the sake of sufficient air feed into the body cavity, the vent passage 6' of the valve body 6 is blocked by completely closing its open end with the bulb of a finger after starting the air supply such as an air pump, the whole quantity of the air collected in the valve casing 9 flows into the outlet air pipe 4.sub.1, and consequently a jet of air is fed into the body cavity as well as shot against an objective lens from the air feed-water feed nozzle 3.
Then, gradually opening the open end of the vent passage 6' by moving the finger either upwardly or laterally, the quantity of air escaping into the atmosphere increases in accordance with the degree of the opening.
On the other hand, when the valve body 6 is pushed down against the helical compression spring 7 until the annular groove 6" is aligned with both of the intake and outlet water pipes 5.sub.2, 5.sub.1, then the communication between the intake and outlet air pipes 4.sub.2, 4.sub.1 is interrupted by the bottom part of the valve body 6 so as to stop the jet of air from the air feed-water feed nozzle 3. Simultaneously, water from the intake water pipe 5.sub.2 flows through the annular groove 6" into the outlet water pipe 5.sub.1 and a jet of water is shot against the objective lens.
In the event of intending to expel all of the air which has collected in the valve casing 9, a part of this air is forced to flow into the outlet air pipe 4.sub.1 and thence into the body cavity from the air feed-water feed nozzle 3.
The reason why the whole quantity of air does not always escape into the atmosphere through the vent passage 6' is that the vent passage 6' imposes resistance against air flow therethrough.